This invention relates to electronic equipment for orienting the data trace from a recirculating memory to the display apparatus such that the otherwise "moving" trace becomes stationary on the display. Such apparatus is advantageously incorporated in apparatus for synchronously defibrillating a patient.
In defibrillators, electrical depolarizing impulses of high voltage are used to revert certain arrhythmias in the heart beat and thereby re-establish a more normal heart function. It is known that application of the depolarizing impulse at the wrong time of a beat cycle can cause cardiac arrest, thus, it is desirable to check the point in the cardiac cycle for the application of the defibrillating pulse. In order to check the cardiac cycle, an ECG display is utilized which will show the full waveform of the cardiac cycle. This waveform is normally comprised of a series of characteristic points conventionally designated by the letters P, Q, R, S and T. The Q, R and S portions of the wave, when taken together, are referred to as the QRS complex, or alternatively, the R-wave. Conventional methods and equipment for determining that the R-wave has occurred. An example of such detectors is disclosed in U.S. Pat. No. 3,590,811 issued July 6, 1971 for Electrocardiographic R-Wave Detector.
It has further been found that arrhythmias are preferably treated with the depolarizing impulse at a specific point of the ECG waveform. Therefore, a provision for verifying the trigger point on the ECG wave is often provided in defibrillator apparatus to view the point on the ECG waveform (R-wave) at which time the depolarizing pulse is delivered. This timing of the depolarizing pulse to fall on the proper segment of the ECG waveform is called "synchronizing" in the domain of defibrillating art.
It is conventional to utilize some electronic notation on the ECG cardiac waveform to indicate that point in the cardiac cycle in which the defibrillator or cardioverter is prescheduled to deliver its impulse. Previous techniques utilized vertical markers superimposed on the waveform all of which moved across the display face. We have found, however, that the utilization of such marks can, in fact, become merged into the R-wave in the ECG waveform causing confusion in interpreting the waveform and identifying the necessary synchronizing point.
Additionally, horizontal electronic markers have been used, however, these also are apt to be confusing in that their important time reference is at the intersection of the horizontal marker and the vertical trace.
Brightness marks or spots have additionally been utilized to provide a blip at the synchronizing point. We have found that these additionally cause problems in that there is a strong tendency at the level at which ECG waveform monitors are operated in defibrillating situations, for the spot merely to bloom the trace of the waveform and thus not readily identify the key point on the general trace. The tendency is to overdrive the cathode ray tube at this point and create a blur, washing out the entire waveform. One might suggest that the overall brightness of the display be lowered, however, such defibrillators are often used in brightly lit areas, such as outdoors, and the high brightness is necessary to see the waveform at all.